Normally one end of a workpiece can be clamped in a multijaw chuck of the type described in my copending patent application Ser. No. 584,400 filed Feb. 15, 1984 and entitled "Air-cooled hydraulic power-chuck actuator", and the other end can be supported on center to rotate the workpiece in a lathe so that it can be turned down, polished, or subjected to whatever machining operation is called for. In fact fairly short workpieces can even be held only at one axial end by such a multijaw chuck.
A long workpiece whose entire outer surfaces must be machined is lathed while supported on centers, that is between coaxially confronting conical points that fit with complementarily shaped but coaxially oppositely opening recesses in the workpiece ends. These points are normally mounted in high-velocity bearings so the workpiece and the points, once fitted axially together, can rotate jointly at high speed about the axis which is stationary.
The workpiece supported on center in this manner must be engaged at at least one of its axial end surfaces by a drive element which is rotated at high speed about the axis while being urged axially against the workpiece. It is absolutely essential that the drive element that actually engages the workpiece do so evenly all around the axis, as any imbalance could bend or deform the workpiece. Hence recourse is normally had to a drive plate formed with workpiece-engagement formations or teeth that are angularly equispaced about the axis and radially equispaced therefrom by a distance equal to the workpiece radius. For maximum efficiency it is necessary that the rotational force be transmitted to the workpiece as far from the rotation axis as possible, which can best be done by making sure the drive teeth engage immediately at or adjacent the outer periphery of the workpiece face.
Thus it is necessary for the shop to have a series of different drive face plates, each corresponding to a different workpiece radius. Valuable storage space and equipment money is tied up in this manner. When workpiece radius changes, it is necessary to remove the current face plate and exchange it for one of the new radius. This represents a loss in lathe time and a cut in worker efficiency, producing a more costly product.